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Boron nitride nanosheets (BNNS) were mixed with rutile TiO 2 and (Al, Nb)-codoped ceramics (ANTO) powders by heteroaggregation method. Homogeneous ceramics with the single phase of rutile TiO 2 were obtained by subsequent solid-state sintering. Scanning transmission electron microscope (STEM) and X-ray photoelectron spectrometer (XPS) results show that N was doped into the crystal lattice during sintering. It is shown that the strong electron localization of the covalent N i –O bond formed between interstitial N (N i) and adjacent O atom shifts the cutoff frequency of high permittivity from ∼100 kHz to 100 MHz in both rutile TiO 2 and the ANTO systems. Particularly, the ANTO-0.6BNNS sample exhibits optimum dielectric properties with a permittivity of 1.3 × 104 and tan δ of 0.04 measured at 1 MHz. Meanwhile, the colossal permittivity of ANTO-0.6BNNS with tan δ < 0.1 shows good temperature stability in the temperature range of 200–400 K. [ABSTRACT FROM AUTHOR]

(1- x wt)Bi 0.0025 Nb 0.0025 Ti 0.995 O 2 - x wt Bi 2 Ti 4 O 11 composite ceramics with high permittivity were fabricated by a conventional sintering method. The sintering temperature was decreased from 1300 °C to 1130 °C, and the grain size was reduced from ~2.6 μm to ~1.5 μm by the addition of Bi 2 Ti 4 O 11 phase. When x wt = 0.2, the breakdown strength was increased from 1 kV/cm to 13 kV/cm while preserving high permittivity (ϵ' ~ 1100). Microstructure, I–V behavior, and Impedance spectroscopy studies demonstrated that the enhanced breakdown strength and excellent dielectric properties were attributed to the small grain size and the highly resistant grain boundaries. These advantages, together with its excellent DC bias stability of dielectric constant (0–1050 V/cm), give the composites a great potential in rutile TiO 2 -based high voltage MLCC applications. [ABSTRACT FROM AUTHOR]

Abstract: A solid state reaction of ZrH2, Si3N4 and B4C has been proposed to synthesize machinable ZrB2–SiC–BN composites. Dense ZrB2–SiC–BN composites with fine grain size and homogeneous microstructure were fabricated via spark plasma sintering at 1900°C in vacuum. The kinetics of the reaction process was studied with XRD results. SEM and TEM results showed that the in-situ formed BN phase was composed of micro-sized intergranular and nano-sized intragranular h-BN particles. The influences of the BN content on the mechanical properties as well as the thermal conductivities of the composites were studied. The composites that contained >20vol% BN exhibited excellent machinability and high strength. [Copyright &y& Elsevier]

Abstract: ZrB2–SiC composite powders have been synthesized by combustion synthesis in air, using a mixture of Zr, B4C and Si as raw materials. It was found that the air atmosphere has played an important role in the ignition process of the SHS reaction. Three other kinds of ZrB2–SiC–ZrC composite powders with different ZrC content were also synthesized, and the ignition time has been measured for better understanding the ignition mechanism. As a result, the composite powders with particle size smaller than 1 µm and oxygen content as low as 0.4 wt.% were obtained. [Copyright &y& Elsevier]

Abstract: Binderless WC ceramics were prepared by reactive spark plasma sintering, using tungsten trioxide, tungsten and carbon black as the starting materials. Phase assemblages and microstructure of the as-sintered ceramics were investigated. It was found that graphite existed as an impurity phase due to the volatilization of WO3, and W could compensate for the WO3 loss to form WC with a single phase. Benefiting from the enhanced sinterability, WC ceramics with high relative density and good hardness could be obtained at temperature as low as 1500°C. [Copyright &y& Elsevier]

In this work, 0.99(0.94Bi 0.47 Na 0.47 Ba 0.06 TiO 3 -0.06BiAlO 3)-0.01NaNbO 3 lead-free ceramics were synthesized by means of different methods including conventional solid state sintering (SSS), cold-sintering-assisted sintering (CSS), and spark plasma sintering (SPS) methods. Their microstructure and dielectric properties were studied comparatively. The ceramics via SPS and SSS exhibit pure structure, while a secondary phase exists in the ceramics via CSS. Compared to SSS, CSS and SPS can obviously reduce the processing temperatures for obtaining dense ceramics. The ceramics via SPS have the smallest mean grain size of 80 nm, while those via CSS and SSS exhibit increased grain sizes. The dielectric measurement demonstrates that temperature stability in dielectric constant at high temperatures is affected by sintering methods. The SPS sample shows the poorest temperature stability of permittivity. The ceramics post-annealed at 1050 °C via CSS exhibits the widest temperature range between 49 °C and 412 °C for temperature coefficient of capacitance ≤±15%, which can be expected to be used in the field of high-temperature capacitors. • BNBTA-0.01NN ceramics were prepared via the three methods including SPS, CSS, SSS. • Processing temperatures for obtaining dense ceramics are reduced via CSS and SPS. • Ceramics annealed at 1050 °C via CSS show TCC ≤±15% between 49 °C and 412 °C. • Temperature window of 363 °C is much higher than the requirement of X9R standard. [ABSTRACT FROM AUTHOR]

Textured and platelet-reinforced ZrB2-based ultra-high-temperature ceramics (UHTCs) are prepared via reactive hot pressing and successive hot forging. The textured materials display significantly anisotropic mechanical properties, and the flexural strength has been improved by 52% owing to the orderly arrangement of platelet ZrB2 grains. The texturing of ZrB2-based platelet composites should open up an effective approach to optimizing the properties of ZrB2-based UHTCs. [Copyright &y& Elsevier]